Hitherto, copper alloys, such as Cu—Zn alloys, Cu—Fe alloys that are excellent in heat resistance, and Cu—Sn alloys, have been frequently used for parts of electronic and electric machinery and tools. While inexpensive Cu—Zn alloys have been used frequently, for example, in automobiles, the Cu—Zn alloys as well as Cu—Fe alloys and Cu—Sn alloys have been unable to currently cope with the requirements for use to automobiles, since recent trends strongly require to make the size of terminals and connectors to be as small as possible, and they are mostly used under severe conditions (at a high temperature and under corrosive environments) in an engine room and the like.
In accordance with the changes of working conditions, severe characteristics are required for the terminal and connector materials. While copper alloys that are used in these application fields are required to have various characteristics, such as stress relaxation property, mechanical strength, heat conductivity, bending property, heat resistance, reliable connection to Sn plating, and anti-migration property, particularly important characteristics include mechanical strength, stress relaxation property, heat and electric conductance, and bending property.
The structure of the terminals have been variously devised for ensuring connection strength at the spring parts in relation to miniaturization of the parts. As a result, the materials are more strictly required to be excellent in bending property, since cracks have been often observed at the bent portion in conventional Cu—Ni—Si alloys. The materials are also required to be excellent in stress relaxation property, and the conventional Cu—Ni—Si alloys cannot be used for a long period of time, due to increased stress load on the material and high temperatures in the working environments.
It is indispensable to improve bending property when the alloy materials are used for the automobile connectors. Although improvements of bending property have been investigated in ways, it has been difficult to improve the bending property while maintaining the mechanical strength and elasticity.
Conductivity and stress relaxation property should be balanced since stress relaxation is accelerated due to auto-heating when the materials are poor in heat and electric conductivity.
On the other hand, the following requirements have been also addressed, with respect to improvement in compatibility to plating for plating the copper alloy material for parts of electronic and electric machinery and tools, and in resistance to deterioration of plate after plating (which are collectively called as plating characteristics).
Cu plating is generally applied on the material as an underlayer followed by Sn plating on the surface thereof, for improving reliability when copper-based materials are used for the above automobile connector such as a box-type connector. When unevenness (roughness) of the material surface is larger than the thickness of the plating layer, the plating is repelled from convex portions without being plated to make it impossible to uniformly plate. In addition, the interface area between the material and plating layer is increased to readily cause mutual diffusion between Cu and Sn, thereby the plating layer is readily peeled off due to formation of voids and a Cu—Sn compound. Accordingly, the surface of the material should be as smooth as possible.
While Au is generally plated on the Ni underlayer plating in the terminals or connectors for the electronic and electric appliances such as mobile terminal devices and personal computers, deterioration of the plating layer such as peeling of the plating layer as described above is also caused due to roughness of the surface of the material even when the surface is composed of the Au plating layer and the underlayer is composed of the Ni plating layer.
Accordingly, a copper alloy that satisfies the above plating characteristics as well as various characteristics described above, has been desired.
Other and further features and advantages of the invention will appear more fully from the following description, take in connection with the accompanying drawing.